Tri-tone trim mask for an alternating phase-shift exposure system

ABSTRACT

A photolithographic trim mask includes a transparent region, an attenuated phase-shift region, and an opaque region. The transparent region substantially transmits received light. The attenuated phase-shift region attenuates and shifts the phase of the received light. The phase-shifted attenuated light patterns a coarse line region of a wafer. The opaque region substantially prevents received light from exposing a fine line region of the wafer.

TECHNICAL FIELD

This invention relates generally to the field of photolithography andmore specifically to a tri-tone trim mask for an alternating phase-shiftexposure system.

BACKGROUND

A photolithographic mask may be used to pattern an object such as asemiconductor wafer of an integrated circuit. The mask may be positionedbetween a light source and the object. Light from the light source isselectively transmitted, blocked, or otherwise affected by the mask todefine a pattern on the object. A mask such as an embedded attenuatedphase-shift mask includes attenuated phase-shift regions. An attenuatedphase-shift region transmits a small percentage of light and shifts thephase of transmitted light. Light passing through an attenuatedphase-shift region may destructively interfere with light passingthrough an adjacent transparent region, which may allow for higherresolution pattern definition in certain situations. Embedded attenuatedphase-shift masks, however, do not provide for high resolution patterndefinition in other situations. It is generally desirable to have highresolution pattern definition in a variety of situations.

SUMMARY OF THE DISCLOSURE

In accordance with the present invention, disadvantages and problemsassociated with previous techniques for providing a photolithographicmask may be reduced or eliminated.

According to one embodiment of the present invention, aphotolithographic trim mask for patterning a wafer includes atransparent region, an attenuated phase-shift region, and an opaqueregion. The transparent region substantially transmits received light.The attenuated phase-shift region transmits a portion of received lightand shifts the phase of the transmitted light. The shifted lightpatterns a coarse line region of a pattern. The opaque regionsubstantially prevents received light from exposing a fine line regionof the pattern, where the fine line region is to be patterned by aseparate alternating phase-shift mask.

Certain embodiments of the invention may provide one or more technicaladvantages. A technical advantage of one embodiment may be that a trimmask may include attenuated phase-shift, opaque, and transparentregions. An attenuated phase-shift region may be used to pattern acoarse line region of a pattern. The attenuated phase-shift region mayprovide for higher precision patterning of the coarse line region thanan opaque region can provide. A fine line region of the pattern may beleft unexposed by an opaque region during one exposure, and patterned byan alternating phase-shift mask during a next exposure. The opaqueregion may protect the fine line region from exposure to light, whichmay allow for effective exposure of the fine line region by thephase-shift mask.

Certain embodiments of the invention may include none, some, or all ofthe above technical advantages. One or more other technical advantagesmay be readily apparent to one skilled in the art from the figures,descriptions, and claims included herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and itsfeatures and advantages, reference is now made to the followingdescription, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1A is a diagram illustrating an example mask;

FIGS. 1B and 1C are diagrams illustrating an example trim mask of themask of FIG. 1;

FIG. 1D is a diagram illustrating an example alternating phase-shiftmask of the mask of FIG. 1;

FIG. 2A through 2E illustrate an example mask at different phases of anetching process:

FIG. 2A illustrates a cross-sectional sample of an example mask;

FIG. 2B illustrates the mask of FIG. 2A after an etch process;

FIG. 2C illustrates the mask of FIG. 2B during the formation of a resistlayer;

FIG. 2D illustrates the mask of FIG. 2C after selective removal ofexposed resist layer;

FIG. 2E illustrates the mask of FIG. 2D after removal of the remainingresist layer;

FIGS. 3A and 3B illustrate a cross-sectional view of the exposure of awafer using an example trim mask and an example alternating phase-shiftmask:

FIG. 3A illustrates the exposure of the wafer by the example trim mask;and

FIG. 3B illustrates the exposure of the wafer by the example alternatingphase-shift mask.

DETAILED DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention and its advantages are bestunderstood by referring to FIGS. 1A through 3B of the drawings, likenumerals being used for like and corresponding parts of the variousdrawings.

FIG. 1A is a diagram illustrating an example mask set 10. A mask set mayrefer to one or more photolithographic masks that may be used to patternan object such as a semiconductor wafer. Mask set 10 may be positionedbetween a light source and the object. Light from the light source isselectively transmitted, blocked, phase shifted, or otherwise affectedby mask set 10 to pattern the object. For example, a pattern may bedefined on a resist layer of a wafer to generate features of anintegrated circuit. The size and shape of mask set 10 determine the sizeand shape of the pattern. Mask set 10 may be of any appropriate size orshape for creating a pattern of any suitable size or shape on theobject.

According to one embodiment, mask set 10 may be used to pattern a gatepattern of a circuit such as a CMOS integrated circuit. A pattern mayinclude fine line regions, where the pattern is narrow or requires veryprecise patterning, and coarse line regions, where the pattern is wideor requires significantly less precise patterning. An example of a fineline region includes a gate or transistor region of a CMOS integratedcircuit. A narrow width, precisely controlled polysilicon layer ispatterned to partially cover the active or diffusion regions of asemiconductor substrate to form a gate. An example of a coarse lineregion includes an interconnect region. The interconnect regions atleast partially connect the transistor regions to the external world.Other examples of fine line and coarse line patterning include fineinterconnects coupled with coarse power bussing on a metal layer of anintegrated circuit.

According to the illustrated embodiment, mask set 10 includes a trimmask 20 and an alternating phase-shift mask 22. Trim mask 20 andalternating phase-shift mask 22 may each be used to condition the lightas part of the patterning process. For example, trim mask 20 may be usedto condition the light during a first exposure, and alternatingphase-shift mask 22 may be used to condition the light during a secondexposure.

According to one embodiment, trim mask 20 may include regions that aresubstantially transparent, regions characterized as attenuatedphase-shift regions, and regions that are substantially opaque. Trimmask 20 and alternating phase-shift mask 22 are described in more detailwith reference to FIGS. 1B and 1C.

According to a known technique, a alternating phase/trim mask setincludes an alternating phase mask and a bi-tone trim mask. A bi-tonetrim mask typically has transparent and opaque regions. During a firstexposure, the transparent regions pattern the coarse line regions, andthe opaque regions shield the fine line regions. During a secondexposure, the fine line regions are patterned by the phase mask. Incertain situations, however, the bi-tone trim mask cannot pattern thecoarse line regions with sufficient resolution. According to anotherknown technique, the bi-tone trim mask may include phase-shift maskregions and transparent regions. The phase-shift mask regions of thetrim mask, however, do not sufficiently shield the fine line regions,significantly reducing the contrast and resolution of the fine lineregions.

FIG. 1B is a diagram illustrating example trim mask 20 of mask set 10 ofFIG. 1. Trim mask 20 includes a transparent region 30, an attenuatedphase-shift region 32, and an opaque region 34. Regions 30, 32, and 34may have any suitable size or shape. Transparent region 30 transmitssubstantially all light from the light source. Typically, transparentregion 30 transmits light to allow for removal of a resist layer on awafer. Transparent region 30 may comprise any suitable substantiallytransparent material operable to substantially transmit light, such asquartz. The transparent material may form a substrate for trim mask 20.

Attenuated phase-shift region 32 acts to transmit only a portion of thereceived light to the object. When suitably illuminated, attenuatedphase-shift region 32 shifts the phase of the transmitted light by anamount suitable to produce destructive interference with other lightdiffracted around the edges of the attenuated phase-shift region 32.

Attenuated phase-shift region 32 may comprise any suitable attenuatedphase-shift material. An attenuated phase-shift material may refer to amaterial that transmits approximately two to fifteen percent of receivedlight, and shifts the phase of the transmitted light by, for example,approximately 180°. As an example, an attenuated phase-shift materialmay transmit less than ten percent of the light such as less than eight,six, four, or three percent of the light. An attenuated phase-shiftmaterial may comprise molybdenum silicide (MoSiOxNy), a chromium-basedmaterial, or other suitable material, depending on the wavelength of thepatterning light. Attenuated phase-shift region 32 may be formed by anattenuated phase-shift layer comprising an attenuated phase-shiftmaterial. The attenuated phase-shift layer may be disposed outwardlyfrom the substrate of trim mask 20.

The phase of light passing through attenuated phase-shift region 32 maybe shifted by an amount, typically approximately 180°, with respect tothe phase of light passing through transparent region 30. The lightpassing through attenuated phase-shift region 32 may destructivelyinterfere with light passing through an adjacent transparent region 30.The interference may provide for higher resolution pattern definition orhigher contrast pattern resolution.

Opaque region 34 blocks substantially most or all light to prevent thelight from reaching the object. Typically, opaque region 34 blocks lightin order to leave the resist layer on a wafer unexposed. Opaque region34 may comprise any suitable opaque material operable to substantiallyblock the transmission of light, for example, chromium. Opaque region 34may be formed by an opaque layer comprising an opaque material. Theopaque layer may be disposed outwardly from the substrate of trim mask20.

Opaque region 34 may include other layers, for example, an attenuatedphase-shift layer. For example, the opaque layer may be disposed betweenan attenuated phase shift layer and a transparent substrate, or may bedisposed outwardly from an attenuated phase-shift layer that is disposedoutwardly from a transparent substrate. Opaque region may comprise anysuitable arrangement of layers, with or without the addition of anattenuated phase-shift layer, that blocks substantially most or alldirect transmission of light.

Opaque region 34 is designed to shield fine line regions from the trimmask exposure so that only phase-shift mask 22 substantially exposesthese regions, so the size and shape of opaque region 34 may correspondto the size and shape of phase-shift mask 22. A boundary 36 betweenattenuated phase-shift region 32 and opaque region 34 may be placed suchthat attenuated phase-shift region 32 and phase-shift mask 22 patternthe same regions. Boundary 36, however, may be placed at any suitablelocation.

FIG. 1C is a diagram illustrating another example from mask 50 of maskset 10 of FIG. 1. Trim mask 50 includes tabs 42 and wings 44. Tabs 42extend from the opaque regions to protect end projections of the fineline regions. Tabs 42 may be opaque, attenuated, or a combination ofopaque and attenuated. Wings 44 are extensions that widen the opaqueregion to shield the fine line regions. Wings 44 may be fully opaque,partially opaque, or any suitable combination of opaque and attenuated.A boundary 36 between the opaque and attenuated regions may be placed atthe base 38 of a wing 44. Boundary 36 may be placed at any suitabledistance 40 along an extension that joins a fine line region with acoarse line region. Phase-shift mask 22 may be used to pattern trim mask20 as described with reference to FIGS. 2A through 2C.

FIG. 1D is a diagram illustrating an example alternating phase-shiftmask 22 that includes zero phase regions 26 and pi phase regions 28.Phase-shift mask 22 selectively alters the phase of light to createcontrolled destructive interference that may improve resolution anddepth of focus. Light passing through zero phase regions 26 is 180° outof phase from light passing through pi phase regions 28. Light passingthrough a zero phase region 26 and an adjacent pi phase region 28destructively interfere. Zero phase regions 26 and pi phase regions 28may be created by etching a substrate, such as a quartz substrate, to aprecise depth to create the appropriate phase shift. The depth dependson the wavelength of the light.

Modifications, additions, or omissions may be made to mask set 10without departing from the scope of the invention. As used in thisdocument, “each” refers to each member of a set or each member of asubset of a set.

FIGS. 2A through 2E illustrate an example mask 50 at different phases ofan etching process. FIG. 2A illustrates a cross-sectional sample of mask50 during an initial phase. Mask 50 may include one or more layersdeposited outwardly from an outward surface of a substrate 60. Forexample, an attenuated phase-shift layer 64 may be deposited outwardlyfrom the outer surface of substrate 60, and an opaque layer 68 may bedeposited outwardly from the outer surface of attenuated phase-shiftlayer 64. Any suitable order of layers, however, may be used. One ormore passes of a photoresist layer 70 may be deposited outwardly fromeither of the layers and patterned in order to selectively produce theregions of transparent, opaque, and attenuated regions.

According to one embodiment, substrate 60 may comprise any suitabletransparent material such as quartz. Substrate 60 may have any suitablethickness. Attenuated phase-shift layer 64 may comprise any suitableattenuated phase-shift material operable to block most light and toshift the phase of the light approximately 180°. For example, attenuatedphase-shift layer may comprise molybdenum silicide. Attenuatedphase-shift layer 64 may have any suitable thickness. Opaque layer 68may comprise any suitable opaque material operable to substantiallyblock light. For example, opaque layer 68 may comprise chromium. Opaquelayer 68 may have any suitable thickness.

Photoresist layer 70 may comprise any suitable material such as a resinthat is initially insoluble in a developer but becomes soluble when itexposed to light or another energy source. Photoresist layer 70,however, may comprise a material that becomes insoluble when exposed.Photoresist layer 70 may have any suitable thickness. After deposition,resist layer 70 may be cured using any suitable technique such asbaking. Portions of photoresist layer 70 exposed to light may undergowavelength-specific, radiation-sensitive chemical reaction to create ofthe mask pattern of mask 50. Portions of photoresist layer 70 may alsobe exposed by elections, protons, or other charged or unchargedparticles.

Layers may be formed outwardly from substrate 60 using any suitablemethod. For example, layers may be deposited using conventionaloxidation or deposition techniques such as chemical vapor deposition orphysical vapor deposition techniques.

FIG. 2B illustrates mask 50 after an etch process. Mask 50 may be etchedusing any suitable process such as a dry etching technique, a wetetching technique, or both. As an example, if attenuated phase-shiftlayer 64 comprises molybdenum silicide, layer 64 may be dry etched in anreacting ion etching system. As another example, if attenuatedphase-shift layer 64 comprises chromium, attenuated phase-shift layer 64may be wet etched. Photoresist layer 70 may also be removed.

FIG. 2C illustrates mask 50 during the formation of resist layer 72.Resist layer 72 may be deposited outwardly from opaque layer 68 in anysuitable manner. Resist layer 72 is etched to define an opaque region 80and an attenuated phase-shift region 82. Exposure may be by photons,electrons, protons, or other energy transfer. Exposed regions may retainresist to protect underlying region or cause resist to disappearexposing underlying regions.

FIG. 2D illustrates mask 50 after removal of exposed resist layer 72.The exposed resist layer 72 may be removed by any suitable process.Exposed opaque layer 68 may be removed using any suitable etchingprocess to form attenuated phase-shift region 82.

FIG. 2E illustrates sample 50 after removal of the remaining resistlayer 72 to yield opaque region 80. The remaining resist layer 72 may beremoved by any suitable process.

Modifications, additions, or omissions may be made to the method withoutdeparting from the scope of the invention. The method may include more,fewer, or other steps. Additionally, steps may be performed in anysuitable order without departing from the scope of the invention. Forexample, attenuated phase-shift layer 6A may be deposited outwardly fromopaque layer 68. As another example, any suitable exposure process maybe used.

As an example, another embodiment of the method exposes, develops theresist, and then etches into a hard mask. A hard mask may refer to alayer of silicon dioxide on silicon nitride. Then, the method strips theresist, recoats, exposes, develops the resist, and then etches the hardmask. Finally, the hard mask finished pattern is transferred to a lowerlayer of the wafer, and the hard mask is removed.

FIGS. 3A and 3B illustrate a cross-sectional view of the exposure of awafer 104 through lenses 130 using a trim mask 100 and an alternatingphase-shift mask 102. Referring to FIG. 3A, trim mask 100 is disposedbetween a light source 106 and wafer 104. According to the illustratedembodiment, wafer 104 includes a substrate 110, a fine line region 112,and an coarse line region 114. Substrate 110 may comprise any suitablematerial used in integrated devices, for example, silicon. Fine lineregion 112 may, for example, be disposed outwardly from substrate 110.Fine line region 112 may refer to a region of wafer 104 that includes afeature such as a gate. Coarse line region 114 is disposed outwardlyfrom substrate 110. A coarse line region may refer to a region that doesnot include any active features, and may include a field or interconnectregions.

Mask 100 includes an opaque region 122, a clear region 124, and anattenuated phase-shift region 126. Opaque region 122 is disposedoutwardly from substrate 120, and substantially prevents light fromreaching wafer 104. Clear region 124 is disposed outwardly fromsubstrate 120, and substantially transmits light. Attenuated phase-shiftregion 126 is disposed outwardly from substrate 120. Attenuatedphase-shift region 126 transmits less than twelve percent of light fromlight source 106, and selectively shifts the phase of the transmittedlight.

According to one embodiment of operation, light emitted from lightsource 106 travels to clear region 122, opaque region 124, andattenuated phase-shift region 126 of trim mask 110. Clear region 122 andopaque region 124 selectively transmits and blocks, respectively, thelight that patterns fine line region 112 of wafer 104. Clear region 122and attenuated phase-shift region 126 selectively transmits andattenuates and phase shifts, respectively, the light that patternscoarse line region 114 of wafer 104.

Referring to FIG. 3B, phase-shift mask 102 is disposed between lightsource 106 and wafer 104. Light emitted from light source 106 travelsthrough phase-shift mask 102. Phase-shift mask 102 selectively modifieslight 130 that patterns the fine line region 112 of wafer 104. Lightsource 106 for the phase exposure need not be the same as for the trimexposure.

Modifications, additions, or omissions may be made to the method withoutdeparting from the scope of the invention. The method may include more,fewer, or other steps. Additionally, steps may be performed in anysuitable order without departing from the scope of the invention.

Certain embodiments of the invention may provide one or more technicaladvantages. A technical advantage of one embodiment may be that a trimmask may include attenuated phase-shift, opaque, and transparentregions. An attenuated phase-shift region may be used to substantiallypattern a coarse line region. The attenuated phase-shift region mayprovide for higher precision patterning of the coarse line region thanan opaque region can provide. A fine line region may be shielded fromexposure by an opaque region during one exposure, and patterned by analternating phase-shift mask during a next exposure. The opaque regionmay protect the fine line region from exposure to light, which may allowfor effective exposure of the fine-line region by the phase-shift mask.

While this disclosure has been described in terms of certain embodimentsand generally associated methods, alterations and permutations of theembodiments and methods will be apparent to those skilled in the art.Accordingly, the above description of example embodiments does notconstrain this disclosure. Other changes, substitutions, and alterationsare also possible without departing from the spirit and scope of thisdisclosure, as defined by the following claims.

1. A photolithographic trim mask for patterning, comprising: atransparent region comprising a substantially transparent material andoperable to substantially transmit received light; an attenuatedphase-shift region comprising an attenuated phase-shift material andoperable to: attenuate received light; and shift the phase of thereceived light, the phase-shifted attenuated light operable to pattern acoarse line region of a wafer; and an opaque region comprising an opaquematerial and operable to substantially prevent received light fromexposing a fine line region of the wafer.
 2. The mask of claim 1,wherein the attenuated phase-shift region is further operable to shiftthe phase of the received light by approximately one hundred eightydegrees.
 3. The mask of claim 1, wherein the attenuated phase-shiftmaterial comprises molybdenum silicide.
 4. The mask of claim 1, wherein:the coarse line region further comprises an interconnect region; and thefine line region further comprises a gate region.
 5. A photolithographicmask system for patterning, comprising: a trim mask comprising: atransparent region comprising a substantially transparent material andoperable to substantially transmit received light; an attenuatedphase-shift region comprising an attenuated phase-shift material andoperable to: attenuate received light; and shift the phase of thereceived light, the phase-shifted attenuated light operable to pattern acoarse line region of a wafer; and an opaque region comprising an opaquematerial and operable to substantially prevent received light fromexposing a fine line region of the wafer; and an alternating phase-shiftmask operable to pattern the fine line region.
 6. The mask system ofclaim 5, wherein the attenuated phase-shift region is further operableto shift the phase of the received light by approximately one hundredeighty degrees.
 7. The mask system of claim 5, wherein the attenuatedphase-shift material comprises molybdenum silicide.
 8. The mask systemof claim 5, wherein: the coarse line region further comprises aninterconnect region; and the fine line region further comprises a gateregion.
 9. A photolithographic trim mask for patterning, comprising: asubstrate comprising a substantially transparent material operable tosubstantially transmit received light; an attenuated phase-shift layerdisposed outwardly from the substrate, the attenuated phase-shift layercomprising an attenuated phase-shift material operable to: attenuatereceived light; and shift the phase of the received light; an opaquelayer disposed outwardly from the substrate, the opaque layer comprisingan opaque material operable to substantially block received light, theattenuated phase-shift layer and the opaque layer patterned to form anattenuated phase-shift region and an opaque region, the attenuatedphase-shift region operable to pattern a coarse line region of a wafer,the opaque region operable to substantially prevent received light fromexposing a fine line region of the wafer.
 10. The mask of claim 9,wherein the attenuated phase-shift material is further operable to shiftthe phase of the received light by approximately one hundred eightydegrees.
 11. The mask of claim 9, wherein the attenuated phase-shiftmaterial comprises molybdenum silicide.
 12. The mask of claim 9,wherein: the coarse line region further comprises an interconnectregion; and the fine line region further comprises a gate region.
 13. Amethod of making a photolithographic trim mask, comprising: depositingan attenuated phase-shift layer outwardly from a substrate, thesubstrate comprising a substantially transparent material, theattenuated phase-shift layer comprising an attenuated phase-shiftmaterial; depositing an opaque layer outwardly from the attenuatedphase-shift layer, the opaque layer comprising a substantially opaquematerial; patterning the attenuated phase-shift layer and the opaquelayer to yield one or more transparent regions, a transparent regionoperable to substantially transmit light; and patterning the opaquelayer to yield one or more opaque regions and one or more attenuatedphase-shift regions, an attenuated phase-shift region operable toattenuate received light and to shift the phase of the received light,an opaque region operable to substantially prevent light from exposing afine line region of a wafer.
 14. A method of making a photolithographictrim mask, comprising: depositing an opaque layer outwardly from asubstrate, the substrate comprising a substantially transparentmaterial, the opaque layer comprising a substantially opaque material;patterning the opaque layer to yield one or more opaque regions, anopaque region operable to substantially prevent light from exposing afine line region of a wafer; depositing an attenuated phase-shift layeroutwardly from the opaque layer, the attenuated phase-shift layercomprising an attenuated phase-shift material; and patterning the opaquelayer to yield one or more transparent regions and one or moreattenuated phase-shift regions, a transparent region operable tosubstantially transmit light, an attenuated phase-shift region operableto attenuate received light and to shift the phase of the receivedlight, an opaque region operable to substantially prevent light fromexposing a fine line region of a wafer.
 15. A method for patterning,comprising: exposing a semiconductor wafer using a trim mask comprising:a transparent region comprising a substantially transparent material andoperable to substantially transmit received light; an attenuatedphase-shift region comprising an attenuated phase-shift material andoperable to: attenuate received light; and shift the phase of thereceived light, the phase-shifted attenuated light operable to pattern acoarse line region of the wafer; and an opaque region comprising anopaque material and operable to substantially prevent received lightfrom exposing a fine line region of the wafer; and exposing the waferusing an alternating phase-shift mask to pattern the fine line region ofthe wafer.
 16. A system of making a photolithographic trim mask,comprising: means for depositing an attenuated phase-shift layeroutwardly from a substrate, the substrate comprising a substantiallytransparent material, the attenuated phase-shift layer comprising anattenuated phase-shift material; means for depositing an opaque layeroutwardly from the attenuated phase-shift layer, the opaque layercomprising a substantially opaque material; means for patterning theattenuated phase-shift layer and the opaque layer to yield one or moretransparent regions, a transparent region operable to substantiallytransmit light; and means for patterning the opaque layer to yield oneor more opaque regions and one or more attenuated phase-shift regions,an attenuated phase-shift region operable to attenuate received lightand to shift the phase of the received light, an opaque region operableto substantially prevent light from exposing a fine line region of awafer.
 17. A photolithographic mask system for patterning, comprising: atrim mask comprising: a transparent region comprising a substantiallytransparent material and operable to substantially transmit receivedlight; an attenuated phase-shift region comprising an attenuatedphase-shift material and operable to: attenuate received light; andshift the phase of the received light by approximately one hundredeighty degrees, the phase-shifted attenuated light operable to patterncoarse line of a wafer, the coarse line region further comprising afield region, the attenuated phase-shift material comprising molybdenumsilicide; and an opaque region comprising an opaque material andoperable to substantially prevent received light from exposing a fineline region of the wafer, the fine line region further comprising a gateregion; and an alternating phase-shift mask operable to pattern the fineline region.